Cairo was rocked by a series of explosions on Friday, killing at least five people and leaving scores injured.

The first blast came as a booby-trapped car detonated close to the city’s police headquarters, and could be heard kilometers away. Egypt’s Health Ministry said four people were killed and 51 were injured. The blast was reportedly followed by gunfire.

A second explosion apparently targeted police vehicles close to a metro station in the city’s Dokki district. The Associated Press reported that one person was killed and eight wounded at that attack.

The third took place close to a police station in Talbia, but no one was injured. And the fourth, which went off near a movie theater, reportedly killed at least one person.

No one has claimed responsibility for the near-simultaneous attacks, which come a day after five policemen were shot dead by gunmen on motorcycles in Beni Suef province.

Several floors of the police headquarters, which should be one of the best-protected buildings in the city, were wrecked and charred after the strike, and the nearby Islamic Museum and National Archives were also damaged.

As Saturday marks the anniversary of the start of the uprising against then President Hosni Mobarak in 2011, security forces were already on heightened alert, BBC reports.

The banned Muslim Brotherhood is planning protests across the country after Friday prayers.